Preprints
https://doi.org/10.5194/soil-2020-67
https://doi.org/10.5194/soil-2020-67

  17 Nov 2020

17 Nov 2020

Review status: a revised version of this preprint is currently under review for the journal SOIL.

Assessing biogeochemical and human-induced drivers of soil organic carbon to inform restoration activities in Rwanda

Leigh Ann Winowiecki1, Athanase Mukuralinda2, Aida Bargués-Tobella3, Providence Mujawamaria2, Elisée Bahati Ntawuhiganayo2, Alex Mugayi4, Susan Chomba1, and Tor-Gunnar Vågen1 Leigh Ann Winowiecki et al.
  • 1World Agroforestry (ICRAF), Nairobi, Kenya
  • 2World Agroforestry (ICRAF), Kigali, Rwanda
  • 3Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), Umeå, Sweden
  • 4World Vision- Rwanda

Abstract. Land restoration is of critical importance in Rwanda, where land degradation negatively impacts crop productivity, water, food and nutrition security. We implemented the Land Degradation Surveillance Framework in Kayonza and Nyagatare districts in eastern Rwanda to assess baseline status of key soil and land health indicators, including soil organic carbon (SOC) and soil erosion prevalence. We collected 300 topsoil (0–20 cm) and 281 subsoil (20–50 cm) samples from two 100 km2 sites. We coupled the soil health indicators with vegetation structure, tree density and tree diversity assessments. Mean topsoil organic carbon was low overall, 20.9 g kg−1 in Kayonza and 17.3 g kg−1 in Nyagatare. Stable carbon isotope values (d13CV-PDB ) ranged from −15.35 to −21.34 ‰ indicating a wide range of plant communities with both C3 and C4 photosynthetic pathways. Soil carbon content decreased with increasing sand content across both sites and at both sampling depths and was lowest in croplands compared to shrubland, woodland and grasslands. Field-saturated hydraulic conductivity (Kfs) was estimated based on infiltration measurements, with a median of 76 mm h−1 in Kayonza and 62 mm h−1 in Nyagatare, respectively. Topsoil OC had a positive effect on Kfs, whereas pH, sand and compaction had negative effects. Soil erosion was highest in plots classified as woodland and shrubland. Maps of soil erosion and SOC at 30-m resolution were produced with high accuracy and showed high variability across the region. These data and analysis demonstrate the importance of systematically monitoring multiple indicators at multiple spatial scales to assess drivers of degradation and their impact on soil organic carbon dynamics.

Leigh Ann Winowiecki et al.

 
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Leigh Ann Winowiecki et al.

Leigh Ann Winowiecki et al.

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Short summary
Achieving global restoration targets requires scaling of context-specific restoration options on the ground. We implemented the Land Degradation Surveillance Framework in Rwanda to assess indicators of soil and land health, including soil organic carbon (SOC), erosion prevalence, infiltration capacity and tree biodiversity. SOC was low across both landscapes, influenced by sand content and vegetation. Maps of soil erosion and SOC at 30-m resolution with high accuracy.